On the monotonicity of weak searching

Abstract

In this paper, we propose and study two digraph searching models: weak searching and mixed weak searching. In these two searching models, each searcher must follow the edge directions when they move along edges, but the intruder can move from tail to head or from head to tail along edges. We prove the monotonicity of the mixed weak searching model by using Bienstock and Seymour's method, and prove the monotonicity of the weak searching model by using LaPaugh's method. We show that both searching problems are NP-complete. © 2008 Springer-Verlag Berlin Heidelberg.